Wavelengths of semiconductor laser beams used in writing and reading information on optical recording media are in the ranges of 750 to 830 nm for CD-Rs and of 620 to 690 nm for DVD-Rs. In pursuit of a further increased capacity, optical discs using shorter wavelength lasers have been under study. For example, those using a write wavelength of 380 to 420 nm have been studied.
Various kinds of compounds are used to form an optical recording layer of optical recording media for shorter wavelength recording. For example, patent literatures 1 and 2 report trimethine cyanine dyes, and patent literature 3 reports asymmetric trimethine cyanine dyes. However, these compounds contain an inorganic anion and have the problem of poor light resistance.
Patent literature 4 discloses a metal complex having triazole as a ligand. Patent literature 5 describes a dye having a porphyrin skeleton. Patent literature 6 reports an optical recording material and an optical recording medium containing a trimethine cyanine dye and an azomethine complex. However, these compounds are used as they carry an inorganic counter ion and can cause precipitation of a salt, such as Na+PF6−.
Patent literature 7 discloses a triethylamine salt of an azomethine complex, which turned out to have insufficient sensitivity to 380 to 420 nm.
Patent literature 8 discloses a salt between a trimethine cyanine dye and an azomethine complex. However, there is no report about a compound that exhibits both absorption in the range of from 380 to 420 nm and sufficient decomposition behavior.